The present invention relates in general to the field of fabrication of semiconductor devices and, more particularly, to the use of a high nitrogen concentration plasma to remove fluorine from a reactor in which fluorine compounds are utilized in manufacturing.
Without limiting the scope of the invention, its background is described in connection with chemical vapor deposition processes and equipment.
As is well known in the art of semiconductor fabrication, the manufacturing cost of a given integrated circuit is largely dependent upon processing costs, yield factors, and equipment downtime. In the case of chemical vapor deposition processes utilizing fluorine compounds, such as the deposition of tungsten with WF6, fluorine radicals and fluorine compounds such as hydrogen fluoride are released. Since most conventional CVD reactors have internal surfaces fabricated from aluminum, fluorine radicals released during the deposition process tend to react with the aluminum components to form aluminum fluoride particles, especially in the presence of water vapor. The presence of these particles in the reactor can result in serious yield losses. Additionally, the reaction between fluorine radicals and chamber components tends to shorten the useful life of the reactor components and increases equipment downtime.
Efforts to find more inert surfaces capable of withstanding fluorine attack have included the use of anodized aluminum and certain nickel plated components. These efforts have not, however, proven totally satisfactory in alleviating the problems resulting from the formation of aluminum fluoride particles.
While the work in finding materials more resistant to fluorine ion attack continues, there is a strong need for a process that minimizes or eliminates fluorine ions in the reactor. Thus, there exists a need for an improved process for removing fluorine from CVD reactors that addresses the aforementioned problems and drawbacks.
The present invention provides a method for using current semiconductor manufacturing equipment that more adequately meets the demands of VLSI and ULSI integrated circuits. In particular the invention provides a means of removing fluorine from a CVD reactor in order to reduce aluminum fluoride particle contamination and reactor component wear.
In one embodiment, the invention provides a method of in-situ cleaning of a reactor to remove fluorine. Subsequent to a deposition step in the fabrication of a semiconductor device, for example, the deposition of tungsten with WF6, the reactor is cleaned by injecting a gaseous plasma mixture of nitrogen and hydrogen into the reactor, the volume ratio of nitrogen to hydrogen being in the range of from 2.5:1 to 4.5:1. In one application the volume ratio of nitrogen to hydrogen injected into the reactor is 3.5:1.
The duration of the cleaning may be determined as a function of the thickness of a material deposited upon a wafer during a semiconductor fabrication process. The deposited material may be a metal, such as tungsten, or a dielectric, such as silicon oxide or silicon nitride. In a typical application, the period of time that the gaseous mixture is injected into the reactor is about 1.5 to about 2.3 seconds per 100 angstroms of tungsten deposition. In one embodiment, the gaseous mixture is injected into the reactor for 1.5 seconds per 100 angstroms of tungsten deposition. The flow of the mixture of nitrogen and hydrogen to the reactor may also be approximately 25 reactor volumes during the cleaning process.
Typically the cleaning process is conducted under pressures between 700 and 90 mtorr. The gaseous mixture is injected into the reactor for a period of between 1.5 and 2.3 seconds per 100 angstroms of tungsten deposition. An RF discharge of approximately 13.5 MHZ and power settings of from 200 to 250 watts is used to ionize the gaseous mixture. In one application, the cleaning process is conducted under a pressure of 800 mtorr with an RF frequency of 13.5 MHZ, a power setting of 225 watts, and a temperature of approximately 475xc2x0 C.